1. Field of the Invention
The present invention relates to a pattern projection method, a pattern projection apparatus, and a pattern projection mask which are used in lithography for semiconductor integrated circuits or the like, and more particularly relates to such a pattern projection method, apparatus, and mask which image a pattern upon the mask onto a sensitive plate by utilizing irradiation with a beam of charged particles such as an electron beam or an ion beam.
2. Description of the Related Arts
Recently investigation and development of electron beam exposure devices for lithography with which both high throughput and high resolution can be obtained. As methods of exposure for this type of device, in the prior art, methods have been studied in which one or a plurality of dies (each one of which corresponds to a plurality of integrated circuits which are formed upon a single wafer) are imaged as a group. However, with such a method, the fabrication of the mask, which is intended as the master for projection, presents certain problems. Also it is difficult to restrict to an acceptable range the aberration of the optical system over a large optical field such as is required for more than one die, etc., so that there are a lot of problems to be resolved. In this connection, recently a subdivided projection method has been investigated (for example, refer to U.S. Pat. No. 5,260,151 in which one or a plurality of dies are subdivided into small regions which are then imaged). According to such a method, since the range over which irradiation by the electron beam is required to be performed at one time is relatively small, it is possible to restrict the aberration of the optical system, and thereby projection at high resolution and with high accuracy becomes possible.
With the above described subdivided projection method, the pattern which is provided is subdivided into a plurality of regions on the mask, and images thereof are connected together upon the wafer so as to form one continuous connected pattern. Accordingly, there is a danger that deviations of the positions for projection each time from the positions which were intended, and therefore mutual mis-alignment of the connecting portions of the pattern, may occur, due for example to optical distortion of the small regions on the mask, wobbling of the stages which move the mask and the wafer, electrical fluctuations, errors in the manufacture of the mask, etc . . . For example, if this type of deviation occurs when imaging a wiring pattern, the electrical resistance of the deviated portion is altered, and the characteristics of the device which is obtained become unpredictable.